1. Field of the Invention
The present invention relates to a semiconductor device test system and a semiconductor device test method for specifying a leakage portion on the wiring of a semiconductor device such as an LSI (large scale integrated circuit). The present invention particularly relates to a semiconductor device test system and a semiconductor device test method for specifying a leakage portion on a semiconductor device by applying a current and a magnetic field to the semiconductor device and detecting a stress generated thereby.
2. Description of the Related Art
Recently, semiconductor devices tend to be very small in size and highly integrated. Due to this, if a leak current occurs to a wiring in a semiconductor device, it becomes more difficult to specify a leakage portion.
Now, by way of example, a conventional test system and a conventional test method for specifying the leakage portion of a semiconductor device will be shown. The test system and the test method specify a portion to which a leak current occurs by detecting a magnetic field generated by the leak current.
FIG. 1 is a block diagram showing the constitution of this test system. A stage 54 is provided in a testing section 50. A semiconductor device 55 to be tested is mounted on the stage 54. A microscope 51 for observing the wiring pattern of the semiconductor device 55, an image detector 52 for converting an image obtained by the microscope 51 into an electrical signal and a light source 53 for illuminating the semiconductor device 55 are arranged above the stage 54 and the semiconductor device 55. Also, a magnetic field measuring terminal 58 for detecting a magnetic field generated from the semiconductor device 55 is provided in the testing section 50.
Meanwhile, a power supply 57 for allowing current to flow the semiconductor device 55 is provided outside of the testing section 50. There is also provided a position controller 62 into which the detection signal of the image detector 52 is inputted, for moving the microscope 51, the image detector 52 and the light source 53 based on this detection signal and controlling their positions. Further, a signal outputted from the magnetic field detection terminal 58 is inputted into a magnetic field detector 59. Besides, there is provided a control computer 60 for controlling the position controller 62, the magnetic field detector 59, the light source 53 and the stage 54. The input and output signals of the control computer 60 are inputted into and outputted from each of the position controller 62, the magnetic field detector 59, the light source 53 and the stage 54. There is further provided an image processor 63 for recognizing and processing, as images, the wiring pattern of the semiconductor device 55 obtained by the image detector 52 and a magnetic field detection result about the semiconductor device 55 obtained by the magnetic field detector 59. A signal outputted from the control computer 60 is inputted into the image processor 63. The output signal of the image processor 63 is inputted into an image display unit 64 and displayed thereon as an image. An instruction signal is inputted into the control computer 60 by an input unit 61.
Next, a semiconductor device test method using the test system shown in FIG. 1 will be described. FIG. 2 is a flow chart showing procedures for this test method. First, as shown in a step S401 of FIG. 2, a defective semiconductor device 55 is mounted on the stage 54 shown in FIG. 1. Next, as shown in a step S402, instructions for controlling the positions of the microscope 51, the image detector 52 and the light source 53 and the position and inclination of the stage 54 are inputted into the control computer 60 by the input unit 61. The input signal is outputted from the control computer 60 and inputted into the position controller 62 to control the positions of the microscope 51, the image detector 52 and the light source 53. In addition, this input signal is inputted into the stage 54 to control the position and inclination of the stage 54. Thereafter, using the microscope 51, the wiring pattern of the semiconductor device 55 illuminated by the light source 53 is observed and a wiring pattern image is picked up. Next, the image detector 52 converts the pattern image obtained by the microscope 51 into an electrical signal. Then, the image detector 52 outputs the electrical signal to the image processor 63 through the control computer 60. The image processor 63 recognizes the pattern image as an image and outputs the pattern image to the image display unit 64. The image display unit 64 displays the pattern image. Thereafter, as shown in a step S403, the image processor 63 records this pattern image data.
Then, as shown in a step S404, a current is inputted from the power supply 57 into the wiring of the semiconductor device 55 to turn the semiconductor device 55 into a defective operation state. As shown in a step S405, the magnetic field measuring terminal 58 detects a magnetic field generated on the wiring of the semiconductor device 55. Next, as shown in a step S406, the magnetic field measuring terminal 58 converts the detected magnetic field into an electrical signal and feeds the electrical signal to the magnetic field detector 59. The magnetic field detector 58 processes the electrical signal and outputs the resultant electrical signal to the image processor 63 through the control computer 60. The image processor 63 creates a magnetic field image based on this output signal and feeds the created image to the image display unit 64. The image display unit 64 displays the magnetic field image. Then, as shown in a step S407, the image processor 63 records the magnetic field image. As shown in a step S408, the image processor 63 creates a synthetic image by superposing the magnetic field image on the previously recorded pattern image. Then, as shown in a step S409, the image display unit 64 displays this superposed image. Next, as shown in a step S410, the data analysis of this synthetic image is performed to thereby specify a leakage portion.
Furthermore, as another conventional test method, Japanese Patent Unexamined Application Publication No. 6-314726 discloses a method of applying a magnetic field in perpendicular direction to the wiring of a defective semiconductor device while voltage is being applied to the device, irradiating the wiring with primary electrons and detecting secondary electrons. According to this method, it is possible to measure a leak current value from the potential difference in the width direction of the wiring.
The above-stated conventional techniques have, however, the following disadvantages. According to the method of detecting a magnetic field generated by a leak current, a magnetic field derived from a leak current and that derived from a normal current are included in detected magnetic fields. Due to this, the magnetic field generated by the leak current is often cancelled depending on the manner in which the normal current flows, with the result that a leakage portion cannot be disadvantageously specified.
Furthermore, according to the method disclosed by Japanese Patent Unexamined Application Publication No. 6-314726, if a leakage portion is covered with another wiring, primary electrons do not reach the leakage portion and the leakage portion cannot be, therefore, disadvantageously specified.
It is an object of the present invention to provide a semiconductor device test system and a semiconductor device test method capable of showing a leak current while separating the leak current from a normal current and accurately specifying a leakage portion even if the leakage portion is covered with another wiring.
A semiconductor device test system for specifying a portion of a semiconductor device in which leak current occurs, comprises: a magnetic field generator for applying magnetic field to said semiconductor device; a power supply for allowing current to flow through a wiring of said semiconductor device in said magnetic field; a stress detector for detecting a stress occurring to said wiring by allowing current to flow in said magnetic field and outputting stress image data; an observation unit for observing a wiring pattern of said semiconductor device and outputting wiring pattern image data; and an image display unit for displaying stress images and wiring pattern images based on said stress image data and said wiring pattern image data, respectively.
In the present invention, a current is inputted into the wiring of the semiconductor device while applying a magnetic field to the semiconductor device. By doing so, a stress corresponding to the current is generated on the wiring and the stress is detected. As a result, a leakage portion can be specified. Also, it is possible to detect the direction of the leak current from the direction of the stress. Further, since the stress generated by the magnetic field and the current is detected, a leakage portion can be specified even if the leakage portion is located under another wiring.
Further, the above-stated semiconductor device test system preferably comprises: a storage device for storing said stress image data and said wiring pattern image data; and an image processor for processing said stress image data and said wiring pattern image data, and for creating a superposed image of said images and a difference image among said images. If so, it is possible to specify a leakage portion more accurately, more efficiently.
Furthermore, the magnetic field generator preferably generates a plurality of magnetic fields in different states. If so, it is possible to further improve testing accuracy.
A semiconductor device test method for specifying a portion of a semiconductor device to which portion a leak current occurs according to the present invention, comprises the steps of: applying a magnetic field to the semiconductor device; allowing current to flow through a wiring of the semiconductor device in the magnetic field; detecting a stress occurring to the wiring and creating a stress image by allowing current to flow the wiring of the semiconductor device in the magnetic field; creating another stress image as a comparison stress image; creating a difference image between the stress image of the semiconductor device and the comparison stress image; and comparing the difference image with a wiring pattern image of the semiconductor device.
Also, a plurality of magnetic fields in different states are preferably used as the magnetic field.
Moreover, in the above-stated semiconductor device test method, a same magnetic field and a same current as the magnetic field and the current applied to the semiconductor device are applied to a good semiconductor device same in type as the semiconductor device and a stress occurring to the wiring is detected, thereby making it possible to create the comparison stress image.
Further, a same magnetic field as the magnetic field applied when the stress image is created, is applied to the semiconductor device, and a current is applied to a wiring of the semiconductor device so as to turn the semiconductor device into a good operation state and a stress generated at this time is detected, thereby making it possible to create the comparison stress image.
Additionally, the comparison stress image may be created by a simulation presuming a good operation state of the semiconductor device.
On the other hand, the wiring pattern image may be created based on design data on the semiconductor device.
In the present invention, a specific magnetic field is applied to a defective semiconductor device while applying thereto a current and a generated stress is compared with that of a good semiconductor device, whereby a leak current and a normal current flowing in the semiconductor device can be shown while separating the currents from each other. As a result, it is possible to specify a current leakage portion in the semiconductor device. In addition, the test system and the test method according to the present invention allow knowing the direction of a leak current and specifying a leakage portion even if the leak current occurs to a portion covered with another wiring.